#include<iostream>

using namespace std;
int sum(int a,int b)
{
    int cou=0;
    for(int i=a;i<=b;i++) cou+=i;
    return cou;
}
int main()
{
    int l,r;
    cin>>l>>r;
    cout<<sum(l,r)<<endl;
    return 0;

}